A259178 Numbers k such that (4^k - 1)/3 is squarefree.

1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 16, 17, 19, 22, 23, 24, 25, 26, 28, 29, 31, 32, 33, 34, 35, 37, 38, 39, 41, 43, 44, 46, 47, 48, 49, 51, 52, 53, 56, 57, 58, 59, 61, 62, 64, 65, 66, 67, 69, 71, 73, 74, 75, 76, 77, 79, 82, 83, 85, 86, 87, 88, 89, 91, 92, 93, 94, 95, 96, 97, 98, 101, 102, 103, 104, 106, 107, 109, 111

Offset: 1

Author

Omar E. Pol, Aug 02 2015

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..467

Crossrefs

Complement of A260042.

Cf. A002450, A005117, A008966.

Programs

Magma

[n: n in [1..115] | IsSquarefree((4^n-1) div 3)]; // Vincenzo Librandi, Aug 03 2015

Mathematica

Select[Range[0, 120], SquareFreeQ[((4^# - 1) / 3)] &] (* Vincenzo Librandi, Aug 03 2015 *)

PARI

isok(k) = issquarefree((4^k-1)/3); \\ Michel Marcus, Feb 25 2021